1. Field of the Invention
The present invention relates to a data transmission apparatus capable of data transmissions with and/or without error control and more specifically to automatic recognition of whether or not a remote data transmission apparatus has an error control function.
2. Description of the Prior Art
In data transmission using an ordinary telephone network, the probability of mistaking data is very low, thereby allowing minimal error detection. Hence a data transmission apparatus is sufficient to modulate and demodulate only. In contrast, mobile data transmission using a mobile telephone and the like which often undergoes data error due to fading, etc., requires a very high performance error control system. Such data transmission apparatus is thus in need of a highly accurate error control function in addition to the modulation and demodulation function described above. Data transmission is therefore made impossible between a data transmission unit which effects mobile transmission using a mobile telephone, etc., and one which effects data transmission using an ordinary telephone network, requiring separate channel equipment.
To solve the difficulty, a data transmission apparatus has hitherto been proposed which can automatically recognize whether a remote data transmission apparatus is for mobile data transmission or a data transmission modem directed to an ordinary telephone network.
A conventional apparatus of the type described above selects between a mobile data transmission modulator/demodulator unit and an ordinary telephone network modulator/demodulator unit on the basis of carrier frequencies of incoming input signals after demodulation detected by a carrier detector part. Among the carrier frequencies, one is for mobile data transmission (mobile telephone channel) where data transmission is effected utilizing error control, and another is for ordinary telephone network data transmission where data transmission is effected without error control. These carrier frequencies are different from each other so as to be discriminated.
In view of the drawbacks of the conventional data transmission apparatus, it is an object of the present invention to provide a data transmission apparatus and method capable of both data transmissions each with and/or without error control.